Biology Chapter on DNA and Bacteriophages
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Questions and Answers

What is the primary purpose of a bacteriophage?

  • To infect bacteria (correct)
  • To generate energy
  • To infect plants
  • To produce vaccines

    • Hershey and Chase used radioactive sulfur to track the DNA of the bacteriophage during their experiment.

    False

    What method did Hershey and Chase use to separate the phage coat from the bacterial cells?

    Blender

    The virus that infects bacteria is called a ______.

    <p>bacteriophage</p> Signup and view all the answers

    Match the following individuals with their contributions to the understanding of DNA:

    <p>Hershey and Chase = Experiment confirming DNA as genetic material Avery = Found that DNA carries genetic information Chargaff = Analyzed base composition of DNA Watson and Crick = Proposed the double helix structure of DNA</p> Signup and view all the answers

    What is the primary function of DNA?

    <p>To store genetic information</p> Signup and view all the answers

    Eukaryotic DNA is located in the nucleoid.

    <p>False</p> Signup and view all the answers

    What structure maintains DNA's arrangement inside the cell?

    <p>Gyrase</p> Signup and view all the answers

    DNA consists of a phosphate group, deoxyribose, and __________.

    <p>nitrogenous bases</p> Signup and view all the answers

    Which process occurs during the S-phase of Interphase?

    <p>Replication of DNA</p> Signup and view all the answers

    Match each type of organism with its corresponding DNA structure:

    <p>Eukaryotes = Multiple linear chromosomes Prokaryotes = Single circular chromosome</p> Signup and view all the answers

    DNA analysis can be used for tracing genealogy.

    <p>True</p> Signup and view all the answers

    What are the two types of reproduction mentioned in relation to DNA inheritance?

    <p>Asexual and sexual reproduction</p> Signup and view all the answers

    What is the structure maintained by an enzyme called gyrase?

    <p>Chromatin</p> Signup and view all the answers

    Euchromatin is a region of DNA that is tightly compacted.

    <p>False</p> Signup and view all the answers

    Who contributed to the understanding of the Chromosomal Theory of Inheritance?

    <p>Walter Sutton and Theodor Boveri</p> Signup and view all the answers

    A nucleosome is tied to the next one with the help of __________.

    <p>linker DNA</p> Signup and view all the answers

    Which of the following statements about heterochromatin is correct?

    <p>It is tightly compacted.</p> Signup and view all the answers

    Match the scientists with their contributions to the understanding of DNA:

    <p>Mendel = Pea Plant Experiment Griffith = Transformation Experiment Watson &amp; Crick = Double-Helix Model Franklin = X-Ray Crystallography</p> Signup and view all the answers

    Darwin's Origin of Species was published in 1839.

    <p>False</p> Signup and view all the answers

    What experiment did Avery conduct in 1944?

    <p>Degradation Experiment</p> Signup and view all the answers

    What type of bacteria was responsible for causing disease in Griffith's experiment?

    <p>S-strain bacteria</p> Signup and view all the answers

    Griffith's experiment demonstrated that heat-killed bacteria could transform harmless bacteria into a harmful form.

    <p>True</p> Signup and view all the answers

    What was discovered to be the molecule of heredity in Avery's experiments?

    <p>DNA</p> Signup and view all the answers

    In Griffith's experiment, the harmless bacteria were referred to as the ______ strain.

    <p>R</p> Signup and view all the answers

    Match the following test tubes with their outcomes in Avery's experiment:

    <p>Test Tube #1 = Mice died Test Tube #2 = Mice died Test Tube #3 = Mice died Test Tube #4 = Mice remained healthy</p> Signup and view all the answers

    Which enzyme was used in Test Tube #4 during Avery's experiment?

    <p>DNA-degrading enzyme</p> Signup and view all the answers

    Avery's experiment showed that proteins were the hereditary material.

    <p>False</p> Signup and view all the answers

    What process describes the uptake of external DNA that changes a cell's characteristics?

    <p>Transformation</p> Signup and view all the answers

    What is the primary structure of DNA as determined by Watson and Crick?

    <p>Double-helix</p> Signup and view all the answers

    Adenine pairs with Cytosine in DNA.

    <p>False</p> Signup and view all the answers

    What model of DNA replication was confirmed by the experiment designed by Meselson and Stahl?

    <p>Semi-conservative</p> Signup and view all the answers

    During DNA replication, each double-stranded DNA includes one __________ strand and one new strand.

    <p>parental</p> Signup and view all the answers

    Match the following scientists with their contributions to DNA research:

    <p>James Watson = Proposed the double-helix model Francis Crick = Worked with Watson on DNA structure Matthew Meselson = Conducted experiments on DNA replication models Franklin Stahl = Partnered with Meselson for replication experiments</p> Signup and view all the answers

    What is the main complementary pairing rule for nitrogenous bases as described?

    <p>Adenine pairs with Thymine and Guanine pairs with Cytosine</p> Signup and view all the answers

    Franklin was able to see DNA with the naked eye.

    <p>False</p> Signup and view all the answers

    Which nitrogenous base was found in similar quantities to adenine according to the findings?

    <p>Thymine</p> Signup and view all the answers

    Franklin used _______ diffraction to study the DNA structure.

    <p>X-ray</p> Signup and view all the answers

    Match the organism with its adenine percentage:

    <p>E. Coli = 24.7% Yeast = 31.3% Human #1 = 30.9% Herring = 27.8%</p> Signup and view all the answers

    Which organism had the highest percentage of guanine?

    <p>E. Coli</p> Signup and view all the answers

    The variation in DNA among individuals leads to differences within a species.

    <p>True</p> Signup and view all the answers

    What structural shape of DNA was identified by Franklin?

    <p>Helix</p> Signup and view all the answers

    Study Notes

    DNA Structure

    • DNA is deoxyribonucleic acid, a macromolecule also known as a polynucleotide or nucleic acid.
    • It's the genetic material of cells, carrying instructions for making proteins.
    • DNA is made of nucleotides.
    • Nucleotides contain a nitrogenous base (adenine, thymine, cytosine, or guanine), a pentose (5-carbon) carbohydrate (deoxyribose), and a phosphate group.
    • DNA forms a double helix, with two strands running anti-parallel.
    • Specific bases always pair: adenine with thymine, and guanine with cytosine.
    • These pairs are held together by hydrogen bonds.
    • Each nucleotide is linked by phosphodiester bonds.

    DNA Functions

    • DNA stores genetic information (in eukaryotes, it's in the nucleus; prokaryotes have a nucleoid).
    • DNA is copied during the S phase of interphase and through replication.
    • Gene expression controls protein production, using instructions encoded in DNA.
    • DNA is universal in heredity, transmitting genetic information to the next generation.
    • DNA analysis is used in various fields, including forensics (identifying criminals), identifying pathogens, tracing disease outbreaks, diagnosing diseases like cancer, and tracing genealogy (both within and between species).

    DNA Arrangement & Packaging

    • The genome is a cell's complete genetic information.
    • DNA is too large to fit inside a cell unraveled; therefore, it is supercoiled, packaged tightly.
    • DNA is organized into chromosomes, which are passed down during asexual or sexual reproduction.
    • Sexual reproduction involves two parents, producing sex cells called gametes, which contain one homologous chromosome from each parent.
    • Chromosomes contain genes which code for proteins.
    • Eukaryotes have multiple linear chromosomes; prokaryotes have one circular chromosome.
    • DNA is supercoiled by histones which creates the structure of nucleosomes.
    • Nucleosomes are tied to each other by linker DNA forming a "beads-on-a-string" structure.
    • Multiple nucleosomes are known as chromatin.
    • Euchromatin is a loosely compacted region of DNA containing transcribed genes.
    • Heterochromatin is a tightly compacted region containing genes not actively expressed.

    DNA Timeline

    • Scientific discoveries over time led to our current understanding of DNA.
    • Key events like Redi's experiments, Leeuwenhoek's microscope, Schwann and Schleiden's cell theory, Darwin's theory of evolution, Pasteur's germ theory, Mendel's pea plant experiments, and Sutton and Boveri's chromosomal theory were crucial discoveries.
    • Subsequent experiments like Griffith's transformation experiment, Avery's degradation experiment, Chargaff's base pairing rules, Hershey and Chase's bacteriophage experiments, Franklin's x-ray diffraction photographs, Watson and Crick's double helix model, and Meselson and Stahl's semi-conservative replication experiment played a significant role in explaining the structure and function of DNA.

    Griffith's Experiment

    • Griffith was studying Streptococcus pneumonia bacteria.
    • There are two strains: smooth (S) and rough (R).
    • S strain causes pneumonia (disease); R strain does not.
    • Griffith mixed heat-killed S bacteria with live R bacteria.
    • The mice died and contained live S bacteria, showing a process called transformation.
    • Griffith, however, did not know what the "transforming factor" was at the time.

    Avery, MacLeod, and McCarty Experiment

    • They identified DNA as the transforming factor in Griffith's experiment.
    • They broke down heat-killed S bacteria into their components (proteins, RNA, DNA)
    • They used enzymes that specifically degrade each component and tested each mixture on live R cells.
    • The only mixture that did not transform live R cells to live S cells was the one containing degraded DNA.
    • This demonstrated DNA played a key role in heredity.

    Hershey and Chase Experiment

    • They further confirmed DNA as the genetic material.
    • They used isotopes to label bacteriophage DNA and protein.
    • Labeled the DNA with Phosphorus-32 and protein with Sulfur-35.
    • By separating the phage coats from attached bacterial cells, the researchers could determine which molecules were taken up.
    • Only phosphorus-containing material (DNA) entered the bacteria.

    Chargaff's Rules

    • Chargaff analyzed the base composition of DNA in various organisms.
    • He found a consistent pattern: the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine.
    • This complementary base pairing is crucial to DNA's structure and function.

    Rosalind Franklin

    • She used X-ray diffraction to study DNA structure.
    • Her famous photo 51 provided crucial data for Watson and Crick.
    • Her work showed DNA was a helix shape.

    Watson and Crick

    • Using Chargaff's rules and Franklin's X-ray diffraction data, Watson and Crick built a model of the DNA double helix.
    • The model correctly described the structure of DNA.

    Meselson and Stahl

    • They experimentally determined the semiconservative nature of DNA replication.
    • DNA replication involves each original DNA strand creating a new complementary strand, producing two molecules with one original and one new strands.

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    DNA Discovery PDF

    Description

    Test your knowledge on the fundamental concepts of DNA and bacteriophages with this quiz. It covers key experiments, structures, and functions of DNA, as well as the contributions of significant scientists in the field. Perfect for students studying molecular biology and genetics!

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